That headline may not seem significant, but here's how Pew Charitable Trusts sells its finding that 33 percent of adults who grew up middle class end up sliding downward:

The idea that children will grow up to be better off than their parents is a central component of the American Dream, and sustains American optimism. However, Downward Mobility from the Middle Class: Waking up from the American Dream finds that a middle-class upbringing does not guarantee the same status over the course of a lifetime.

The report, released yesterday, was based on a group of 12,000 participants researchers have followed since 1979. Researchers found that there are a few factors in determening who will move from middle to bottom class.

Divorce is the most significant factor for women; using heroin is it for men. Not having a high school diploma is also a big factor. Here's a graphic that puts it all together:

The racial gap in mobility has perplexed researchers at Pew since a 2007 reportthat said nearly half of African Americans born to middle-income parents in the late 1960s plunged into poverty or near-poverty as adults. That report underscored the feeble grip many African Americans had on middle-class life, prompting researchers to probe deeper, said Erin Currier, project manager of Pew's Economic Mobility Project.

The new report called the performance of blacks on a key standardized test a factor that accounts for virtually the entire mobility gap separating the races. Black males scored much lower than white males on the Armed Forces Qualification Test, which measures reading comprehension, vocabulary and math ability.

"Taking into account differences in AFQT scores between middle-class white and black men reduces the gap until it is statistically indistinguishable from zero," the report said.

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